Let’s look at things from the Russian perspective - yeah, ok, let's do that. But go back further in time to the beginning of the 21st century onwards.
Putin has seen NATO expand further and further into Eastern Europe. He has seen the US put some of its nuclear weapons in non-nuclear NATO member states.
Putin doesn't like this, and over the years has repeatedly tried to raise these issues with the West. However, the West hasn't listened or taken his views seriously.
Why is Putin worried? Well just imagine how Western Europe would feel if Putin gave nuclear weapons to Belarus.
We know how worried JFK was when the USSR put missiles in Cuba.
It's a bit 'double standards' to shit yourself over the Cuban missile crisis then years later dismiss similar concerns from Russia over NATO bases creeping closer and closer to Russia ... don't you think?
BTW, I'm not justifying the Ukraine war. Invading the Ukraine and then shelling the shit out of it is obviously wrong. I'm just doing what you said do - looking at this from a Russian perspective.
Given the above, if you were in Putin’s position, would you start nuclear war now, and almost certainly be incinerated? - no, I wouldn't. But it would be very foolish for Western politicians not to take Putin's threat seriously, or to back him into a corner so much that the nuclear option becomes the only way out for him. Putin is a cold-blooded killer with zero regard for human life. I'm sure he's thought how closely packed Western Europe is (nuking it would be like shooting fish in a barrel). I'm sure he's thought about striking first and wiping out Washington DC, NYC and LA. Putin would have no qualms sacrificing millions and millions of innocent Russians who might get nuked from a retaliatory strike from America. Of course, if Putin ever pressed the big red button, he'd likely go all-in and destroy US cities, and wipe the UK and France off the surface of the planet.
I think a lot of people fall into the trap of thinking that Putin is a Western politician - he's not. Western politicians are leaders, but they have to pose as social workers in order to get elected. Putin doesn't bother with any of that crap - he's one bad bastard.
I also think some people - me included - arrogantly assume that everyone wants to be Westernised. And it's clearly not the case with Putin.